Definitely be sure to check-out the useful diagnostic testing procedures GDI includes on their website here:
http://gdl-online.com/begin1.html#contents
If you're good enough to be able to get to and remove the amp, and if you've got a basic multimeter, you can carry out the recommended procedures and test the basic functioning of the amp, actuator, speed sensor, and the all-important
switch.
While these tests are unlikely to fix anything in and of themselves, they do help to pinpoint the problem(s) and possibly save you bucks (as they did for me last year!)
Good luck...